This invention relates to a process for stabilizing suspensions of inorganic filler powders in polyhydroxyl compounds, particularly polyether polyols, against disintegration. The filler suspensions are stabilized by reaction with small quantities of polyisocyanates at elevated temperature without any adverse effect upon the processibility of the suspensions into polyurethane plastics.
According to an earlier proposal (U.S. Ser. No. 856,075 filed Nov. 30, 1977, & now U.S. Pat. No. 4,207,227, issued June 10, 1980), suspensions of inorganic fillers in polyhydroxyl compounds, particularly polyether polyols, of the type used for producing foamed and unfoamed polyurethane plastics, can be stabilized against disintegration by the addition of a graft polymer of .alpha.,.beta.-unsaturated carboxylic acids and optionally, other comonomers on comparable polyethers. Even small quantities of these graft polymers act as excellent stabilizers when added to the filler suspension at temperatures below 60.degree. C. However, this method of stabilization is unsatisfactory in two respects. On the one hand, the production and use of the stabilizer involves the introduction of another component into the assortment of chemicals used in the production of polyurethanes with all of the problems of storage and logistics. The stabilizer also introduces foreign reactive groups--albeit few, but nevertheless noticeable--into the polyurethane recipe and necessitates for example neutralizing agents, new stabilizers for the foaming reaction, and the like, which the final processor would rather avoid.
Accordingly, the object of the present invention is to make it possible for suspensions of inorganic fillers in polyether polyols to be stabilized solely with the chemicals commonly used in the production of polyurethanes.